The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This invention relates to fluids used in treating a subterranean formation. In particular, the invention relates to the use of water-in-water emulsions which are low viscosity pumpable liquids on the surface, but which form stiff gels downhole useful for isolation of a zone or zones in subterranean formations.
Various types of fluids are used in operations related to the development and completion of wells that penetrate subterranean formations, and to the production of gaseous and liquid hydrocarbons from natural reservoirs into such wells. These operations include perforating subterranean formations, fracturing subterranean formations, modifying the permeability of subterranean formations, or controlling the production of sand or water from subterranean formations. The fluids employed in these oilfield operations are known as drilling fluids, completion fluids, work-over fluids, packer fluids, fracturing fluids, stimulation fluids, conformance or permeability control fluids, consolidation fluids, and the like. Stimulation operations are generally performed in portions of the wells which have been lined with casings, and typically the purpose of such stimulation is to increase production rates or capacity of hydrocarbons from the formation.
Frequently, multiple desired stimulation locations exist in a formation. Sealing devices, such as packers or plugs are usually employed to permit each location to be separately stimulated. This is desirable so that the stimulation operation for each location may be designed for that location, for example, by designing specific flow rates and pressures into the formation. These devices, as well as the casing and cement in the wellbore, prevent loss of stimulation fluids at the location. However, such devices are bulky, expensive, and can be otherwise undesirable. Further, some portions of the well are not cased and cement lined. Conventional sealing devices are not easily used in such areas of the wellbore, and the sealing devices which exist for such use, tend to be less reliable, i.e., inflatable packers.
While various systems have been attempted to seal zones of the wellbore using chemicals such as foams, or gels, such materials have been difficult at best to place into the wellbore, because of the high viscosity of such materials or handling and mixing requirements. High viscosity materials cannot be easily pumped, and many two-part resin systems involve hazardous chemicals such as isocyanate compounds. Many conventional systems are based on crosslinking chemistry, but these have not been wholly satisfactory in form or delivery.
It would be desirable to have a gel system which is low viscosity and pumpable at the surface, and does not require handling or mixing of hazardous materials. This need is met at least in part by the following invention.